1. Field of the Invention
The present invention relates to paper machines, and, more particularly, to wear indicators for seal strips used in a suction box.
2. Description of the Related Art
Paper machines generally include a wet end and dry end of the machine. The wet end of the machine generally can be broken down into further components, such as the head box, forming section, press section, etc. Likewise, the dry end of the machine can be broken down into further components including a dryer section, winder, etc. The wet end of the machine typically includes a number of suction roll assemblies. A suction roll assembly typically includes a suction roll and suction box placed within the suction roll. The suction roll includes a perforated cylindrical shell that is rotatably supported together with the stationary suction box disposed internally thereof and connected with a source of vacuum. The suction box includes a slot like structure along one side thereof and seal strips along each side of the slot for engagement with the inside diameter of the rotating suction roll in order to provide a sealing engagement between the suction box and the inside diameter of the suction roll, so that a vacuum pressure is induced on the vacuum box in communication with the inside diameter of the suction roll to remove water which passes through the roll.
A seal strip assembly, as described above, typically includes a slot or groove along an outer edge facing the inside diameter of the suction roll which receives the seal strips therein. The seal strips are slidably moveable within the slot toward and away from the inside diameter of the suction roll. A loading tube is disposed between the bottom edge of the seal strip and the bottom edge of the slot to pneumatically or hydraulically bias the seal strip into sealing engagement with the inside diameter of the suction roll. Due to frictional contact between the seal strips and the suction roll, wear occurs on the seal strips and the inside diameter of the suction roll, resulting in a reduced life expectancy for the seal strips. In view of the necessity to shut the machine down while the seal strips are being replaced, the life expectancy of the seal strips is an important criteria of the paper machine.
It is known to provide a seal strip assembly with a sensor arrangement for remotely determining the wear state of the seal strip without having to shut down the paper machine and remove the suction roll and suction box. For example, U.S. Pat. No. 6,436,241 (Persson, et al.) discloses a seal strip assembly with an electrical indicator providing a remote indication of the wear state of the seal strip. The seal strip structure is modified to incorporate a sensor having an electrical coil configuration which detects the distance between the sensor and the inside diameter of the suction roll. This type of sensor arrangement is bulky and therefore requires large seal strips to accommodate the sensor. Moreover, modifying the seal strip affects the structural integrity of the seal strip and may result in early wear and/or failure. Further, providing an active sensor within the seal strip makes it difficult to feed the electrical conductors to an end of the suction roll. Thus, this type of wear state sensor arrangement is expensive, cumbersome, lacks accuracy, and detrimentally affects the structural properties of the seal strip.
What is needed in the art is a wear indicator for a seal strip which is accurate, less expensive, and allows for wear state determination without removal of the suction box.